Topically applied antiperspirant compositions are in widespread use throughout much of the world, in order to enable their users to avoid or minimise visible wet patches on their skin, especially in axillary regions. Antiperspirant formulations have been applied using a range of different applicators, including aerosols, roll-ons, pump sprays, sticks and mushroom applicators, in accordance with the individual preferences of consumers. In some parts of the world, sticks are especially popular. The term stick traditionally indicates a bar of solid material which was usually housed within a dispensing container and which retains its integrity whilst being applied, a firm stick. When a portion of a firm stick is drawn across the skin surface, a film of the stick composition is transferred onto the skin surface. Although the stick has the appearance of a solid article, the material forming the stick usually comprises a structured liquid phase such that a film of the material is readily transferred onto another surface upon contact under pressure.
More recently, the term has been applied to soft solids, which have an apparent solid form during storage, but which flow under mild pressure or shear, so that in use they can be extruded through an aperture or apertures onto a dispensing surface. Soft solids retain their shape for at least 30 seconds if removed under non-shear/stress conditions from a container, but if subjected to shear or stress, their structure is destroyed and no more than a minor fraction of the structure can be reformed within a period of about 24 hours when the shear/stress is removed.
There are typically three classes of antiperspirant sticks, namely suspension sticks, emulsion sticks and solution sticks. Suspension sticks contain a particulate antiperspirant active material suspended in a structured carrier. Emulsion sticks normally comprise an emulsion of an oil phase and a hydrophilic phase containing the antiperspirant active in solution, the continuous phase being structured. In some emulsion sticks, the continuous phase is an oil phase. In solution sticks, the antiperspirant is typically dissolved in the liquid carrier phase which is structured. The liquid phase can comprise water and/or a water-miscible organic solvent. The three categories can be applied to sticks of both firm and soft solids compositions.
Conventionally, many sticks have been structured using naturally-occurring or synthetic waxes, of which typical examples include stearyl alcohol, and hydrocarbon waxes or silicone waxes. Waxes are widely available, and by suitable selection of the waxes themselves and their concentrations in the formulation can effectively obtain either a soft solid or a firm solid. Thus for example, wax-structured sticks are described in an article in Cosmetics and Toiletries, 1990, vol 105, p75-78. However, fatty alcohol or wax structured sticks tend to leave visible white deposits on application to human skin, and the deposits can also be transferred onto clothing by physical contact with the skin. A significant, and possibly growing, proportion of consumers of antiperspirants have indicated displeasure at visible deposits. Accordingly, the antiperspirant industry, including the instant inventors, is devoting considerable time and resources to finding means to ameliorate or overcome the customer perception of whiteness deposits.
A number of alternative structurants to waxes have been proposed. The term "gellant" is often employed instead of "structurant". Where the resultant product is a liquid of increased viscosity rather than a solid or gel, the term "thickener" can also be used. For example, the use of dibenzylidene sorbitol (DBS) or derivatives thereof has been proposed as gellant in a number of publications, such as EP 0512770, WO 92/19222, U.S. Pat. Nos. 4,822,602 and 4,725,430. Formulations containing such gellants can suffer from a number of disadvantages, including instability in the presence of acidic antiperspirants, and comparatively high processing temperatures needed in the production of sticks. Some of such formulations containing such gellants are sticky or tacky.
A combination of an n-acylaminoacid amide and 12-hydroxystearic acid to gel a non-aqueous formulation is described in WO 93/23008 and U.S. Pat. No. 3,989,087. However, high processing temperatures are needed to dissolve the gellants and prevent premature gelling. When applied to the skin the formulation can be difficult to wash off, reformulation to overcome the latter problem can be made impossible by the need for high processing temperature.
In WO 97/11678 to Helene Curtis, Inc, there is described the use of a sterol and particularly lanosterol as gellant, sometimes in conjunction with a starch hydrolyzate derivative for antiperspirant compositions.
In WO 98/34588 to Lancaster Group GmbH, there is described the use of lanesterol as a gellant for oil-based cosmetic compositions, containing a cosmetic active material, of which one listed material is a deodorant, though not exemplified.